The present invention relates to a method of making a turbine engine component having airfoils connected with a shroud ring. More specifically, the present invention relates to the manner in which the shroud ring is formed.
A known turbine engine component is disclosed in U.S. Pat. No. 4,728,258 issued Mar. 1, 1988 and entitled "Turbine Engine Component and Method of Making the Same". This patent discloses making a turbine engine component having an annular array of airfoils disposed between inner and outer shroud rings. In order to minimize thermal stresses during use of the turbine engine component, slip joints are provided between the airfoils and a shroud ring to accommodate thermal expansion of the airfoils relative to the shroud rings.
In making the turbine engine component disclosed in U.S. Pat. No. 4,728,258, airfoils are placed in an annular array with end portions of the airfoils embedded in wax inner and outer shroud ring patterns. The wax shroud ring patterns are covered with ceramic mold material to form a mold. The inner and outer shroud ring patterns are then removed to leave inner and outer shroud ring mold cavities in which inner and outer end portions of the airfoils are disposed.
In order to form the inner and outer shroud ring patterns, one or more airfoils is held in a clamp which accurately positions inner and outer end portions of an airfoil in die cavities. The die cavities have a configuration corresponding to the configuration of segments of the inner and outer shroud rings. Hot wax is injected into the die cavities. The hot wax solidifies to form segments of the inner and outer shroud ring patterns. The airfoils are then placed in an annular array with the shroud ring patterns in abutting engagement. The shroud ring pattern segments are then interconnected with a suitable adhesive or hot wax to form annular inner and outer shroud ring patterns.
Relatively expensive fixtures or tooling is used to grip the airfoils and to position them relative to the die cavities in which pattern wax is molded. If it is desired to change the spatial relationship between the airfoils, relatively expensive fixtures and dies must be fabricated. Thus, there is a substantial initial investment in tooling to accurately position the airfoils and in dies to form cavities in which the shroud ring pattern segments are to be formed. If it is desired to make even a relatively small change in the spatial relationship between the airfoils, for example to change the angle of the airfoils by a small amount, new fixtures and dies must be fabricated.